1. Field of the Invention
The present invention relates to a mold for molding a product in a cavity formed by closing the mold.
2. Description of the Related Art
Optical components such as those for a digital camera, a telescopic lens, and a small-sized high-resolution camera lens for a mobile phone require a high level of accuracy in an eccentricity quantity (referred to as an interplanar eccentricity hereinafter) of each center position of two opposing optical surfaces, a lens thickness, and a shape of the optical surfaces. Of these, accuracy in the shape of the optical surfaces has almost reached a satisfactory level along with an improved accuracy in machining a mold. On the other hand, it is desired to improve accuracy in the interplanar eccentricity and in the lens thickness.
As a mold capable of manufacturing an optical component with high accuracy, for example, as shown in FIG. 9A and FIG. 9B, a mold 500 has been known which has a cavity C provided between a first half 600 and a second half 700 and formed by closing the mold 500, and a product is injection-molded in the cavity (see, for example, Japanese Laid-Open Patent Application, Publication No. 2003-231159, paragraphs 0021-0022, FIG. 1).
The first half 600 includes a first die 610 having a cavity surface 610a; and a body member 620 for holding the first die 610 from outside and having a reversely tapered part 621 on a lower end face 622 thereof on a side of the second half 700.
The second half 700 includes a second die 710 having a cavity surface 710a; and a body member 720 for holding the second die 710 from outside and having a tapered protrusion 721 on an upper end face 722 thereof on the side of the first half 600.
The mold 500 is configured such that, when the reversely tapered part 621 and the tapered protrusion 721 are fitted in with each other, a center axis alignment is achieved between the first die 610 of the first half 600 and the second die 710 of the second half 700.
In the conventional mold 500 described above, as shown in FIG. 9A, if a space S1 is left between the lower end face 622 of the first half 600 and the upper end face 722 of the second half 700, accuracy in the thickness of a product is lowered. Further, if the space S1 is relatively large, a material fed into the cavity C may flow out through the space S1, which results in generating a burr on the molded product. Therefore, as shown in FIG. 9B, the mold 500 is designed so as not to leave any space between the lower end face 622 of the first half 600 and the upper end face 722 of the second half 700, when the mold 500 is closed.
However, if the mold 500 is machined so as to contact the lower end face 622 of the first half 600 with the upper end face 722 of the second half 700, it is difficult to make an inclination of a tapered face of the reversely tapered part 621 exactly the same as that of the tapered protrusion 721, due to an influence of dimensional tolerance during machining. Thus a space S2 in a lateral direction may be disadvantageously left between the tapered faces on the reversely tapered part 621 and the tapered protrusion 721, which results in an inaccurate center axis alignment between the first die 610 and the second die 710 to thereby lower the accuracy in the interplanar eccentricity of the molded product.
As described above, there is a problem in the conventional mold 500 that it is difficult to improve accuracy both in the lens thickness and in the interplanar eccentricity of the product, lowering accuracy in molding the product.
It is desirable to provide a mold having an improved accuracy both in the lens thickness and in the interplanar eccentricity of a product.